They are organized in what is called Les Antiquaires et Galeries d'Art du Quartier Drouot. This is an association of antique and art galleries formed by the dealers who surround the well-known auction house, Hôtel Des Ventes Drouot.
Hôtel de Ventes Drouot is a must if you're interested in antiques. It's a beehive of dealers and buyers. It's a event by itself just looking around and sneaking in the auctionroom while the auction is going on.